Generally, a commercial vehicle such as a truck, a bus, a tractor, and the like, is mounted with an auxiliary brake in order to prevent overheating of a brake drum and a brake lining generated due to a braking force continuously applied to a main brake.
An example of this auxiliary brake includes an exhaust brake decreasing an output of an engine by an exhaust control of an exhaust gas, an engine brake using a load of the engine by gear shifting, an intarder sharing oil pressure of a transmission and forcibly constraining a propeller shaft through a valve opened or closed by a control signal applied from an electronic control unit (ECU), a retarder operated by a principle of an electromagnet and forcibly constraining a propeller shaft through magnetic force generated by a control signal applied from the ECU, and the like.
An apparatus of controlling a brake of a tractor according to the related art first generates maximum baking force through the auxiliary brake and generates braking force exceeding the maximum braking force through the main brake, with respect to a required braking force.
For example, in the case in which braking force of 3000 NM is required, braking force of 2000 NM (maximum value) is allocated to the auxiliary brake, and the remaining braking force of 1000 NM is allocated to the main brake.
Therefore, at the time of braking in the case in which a trailer is mounted, the braking force of the auxiliary brake is larger than that of the main brake, such that a phenomenon that the tractor and the trailer are bent like a jackknife occurs.